1. Field of the Invention
The present invention relates to signal processing. More specifically, the present invention relates to a method and apparatus for the determination of pulsatility and resistivity in blood vessels of living subjects.
2. Background Information
New modalities have been developed for ultrasonic imaging systems in recent years. Specifically, certain "state of the art" systems include a mode wherein a real-time angiography study of a subject under examination maybe performed. Angiography, or the two-dimensional mapping of blood vessels, is a useful technique for diagnosing a variety of pathologies.
One shortcoming of ultrasound angiography techniques is that there is currently no easy way to discriminate between veins and arteries independent of the angle between the direction of flow and Doppler interrogation. This is because ultrasound angiography signals are based upon the power of the processed signal. The power of the processed signal provides no way to discriminate veins from arteries in a living subject because the it is roughly equivalent in both veins and arteries.
One prior approach to discriminating between veins and arteries using color flow Doppler is to look at the sign of the velocity (i.e., direction of flow). This technique is scan orientation-dependent and is therefore subject to error. It also fails in the presence of aliasing. Examination of the velocity waveform in single gate Doppler can discriminate between arteries and veins. This is inconvenient because typical Doppler methods examine only one sample volume at a time. Current systems lack the capability of displaying a two-dimensional region with the arteries and veins clearly discriminated.
Prior art methods of discriminating between veins and arteries using ultrasonic imaging systems has been lacking. Such prior art techniques typically require substantial user intervention (e.g., the moving of the ultrasonic probe during scanning), and moreover, often do not accurately distinguish between veins and arteries. Thus, improved means for distinguishing between veins and arteries in an ultrasonic imaging system, such as in a system capable of performing color studies, is desired.
Furthermore, existing methods provide no information on the spatial distribution of clinically important hemodynamic parameters, such as pulsatility index (PI) and resistance index (RI), both of which have been useful in diagnosing vascular disease and impairment of blood perfusion.